3 Biological molecules Flashcards
What’s the main function of glucose?
Energy source in animals and plants
Monosaccharides join together by?
Glycosidic bonds
What is dehydration synthesis?
Another word for condensation
What happens in a condensation reaction to form 1,4 glycosidic bonds?
A hydrogen atom on one molecule bonds to a hydroxyl group (OH) on another molecule which releases a water molecule- creating a 1,4 glycosidic bond (carbon 1 joined to carbon 4)
What happens in a hydrolysis reaction in carbohydrates?
A molecule of water reacts with the glycosidic bond, breaking the bond
Which disaccharide is made from two alpha glucose molecules?
Maltose
What’s the main function of starch?
Main energy store in plants
What is starch made of?
Mixture of two polysaccharides: amylose and amylopectin
What is the structure of amylose?
Formed by alpha glucose joined together by 1-4 glycosidic bonds.
Long, unbranched chain.
Angle of bond make it a tight cylindrical coil- further stabilised by hydrogen bonding within molecule.
Why is the structure of amylose good?
Makes polysaccharide more compact and much less soluble.
What is the structure of amylopectin?
Branched structure, alpha glucose - has 1-4 and 1-6 glycosidic bonds.
What are the key properties of amylopectin?
Insoluble, branched and compact
Why are the properties of amylopectin good?
Ideally suited for storage roles that they carry out
What is the main function of glycogen?
Main energy store in animals
What’s glycogen made of?
Polysaccharide of alpha glucose
What’s the structure of glycogen?
Very branched where glucose can be added or removed- speeds up processes of storing and releasing glucose molecules.
Coiling/branching means they’re compact
How do triglycerides release energy?
Chemical energy is stored in the fatty acid hydrocarbon tails so lots of energy is released when triglycerides are broken down
How are triglycerides formed?
By condensation of one molecule of glycerol and three molecules of fatty acid
What’s the bond formed between glycerol and fatty acid chains called?
Ester bond
How many molecules of water are released per triglyceride formed?
3 (1 per each ester bond)
How much energy do lipids contain compared to carbohydrates?
Carbohydrates contain half the amount of energy per gram as lipids do
Why are triglycerides insoluble?
Because the fatty acid tails are hydrophobic
Why is the insolubility of triglycerides important in cells?
It means that the cells water potential is not affected by the triglycerides.
This is important because if triglycerides didn’t repel water, the water would enter the cell through the process of osmosis and make the cells swell up.
What are lipid droplets?
How the insoluble triglycerides crowd together as droplets (micelles) in cells because the hydrophobic fatty acid tails face inwards
What’s the difference between the structure of phospholipids and triglycerides?
They are both composed of fatty acid chains attached to glycerol but in phospholipids one of the 3 fatty acid tails is replaced by a hydrophilic phosphate group.
A phospholipid molecule has a hydrophobic and hydrophilic part. What is this kind of molecule called?
An amphipathic molecule
In membranes, where do the fatty acid tails face and what does this mean?
Inwards
Means that water-soluble substances can’t easily pass through the membrane
Where do the hydrophilic heads face in phospholipids?
The outside
What is the list common number of carbon atoms found within fatty acids?
12-18 carbons
What kind of energy do lipids store?
Chemical energy
What is the structure of saturated fatty acids?
Carbon atoms not joined by any double bonds
Saturates because number of H atoms attached to carbon skeleton is maximised
What are saturated fats at room temperature?
Solids
What are saturated fats linked to?
An increased risk of cardiovascular disease in humans
What is the origin of saturated fats?
Animal origin usually (from animals)
Examples of foods with high proportion of saturated fats?
Cream, cheese, butter, other whole milk dairy products and fatty meats
What is the structure of a mono-saturated fat?
One double bond present between carbon atoms
What is the structure of a polyunsaturated fat?
More than one double bond between carbon atoms
Why are unsaturated fats liquids at room temperature?
Double bonds kink the carbon chains so they can’t pack together tightly
What are the chemical elements found in carbohydrates?
Carbon, hydrogen and oxygen
What are the chemical elements found in lipids?
Carbon, hydrogen and oxygen
What are the chemical elements found in proteins?
Carbon, hydrogen, oxygen, nitrogen, sulfur
What are the chemical elements found in nucleic acids?
Carbon, hydrogen, oxygen, nitrogen and phosphorus
What are the uses of water?
As a reactant in cells (e.g. photosynthesis, hydrolysis)
Provides structural support in cells
Keeps organisms cool to maintain optimum body temperature
What are the properties of water?
Good metabolite High heat of vaporisation High heat capacity Good solvent Cohesive properties
What is a water molecule made from?
One oxygen atom
Two hydrogen atoms
Why is water a polar molecule?
Oxygen atoms are slightly negatively charged and the hydrogen atoms are slightly positively charged
What is hydrogen bonding between water molecules?
The polarity of water molecules means that a hydrogen atom (+) on one water molecule is attracted to the oxygen atom (-) on another water molecule
Why is O slightly neg and H slightly pos in a water molecule?
H shares a pair of electrons with O. O has a greater affinity for elections than H so ‘pulls’ electrons closer making it slightly negative
Why is water a good metabolite?
Water is used or formed in many metabolic reactions such as condensation and hydrolysis
What is the latent heat of vaporisation?
The amount of energy needed to change one gram of liquid substance to a gas
Why does water have a high heat of vaporisation and why is this good?
As liquid water heats up, hydrogen bonding makes it difficult to separate the water molecules from each other. This means that a lot of energy is needed for water to evaporate.
When water evaporates, energy is used up- this cools the environment where the evaporation is taking place. This is why sweating helps with body temp regulation.
What is specific heat capacity?
The amount of heat one kg of a substance must absorb or lose to change its temp by 1 degree Celsius
Why is it beneficial that water has a high heat capacity?
It takes a long time to heat and cool. This makes it a stable habitat and means that internal temp changes in body are minimised- easier to achieve a stable body temp.
Water is used by warm blooded animals to evenly disperse heat in their bodies
Why is water a good solvent?
Ions and polar molecules can easily dissolve in it.
Water is a polar molecule- means that + end of water molecule attracts - ions and - end will attract + ions.
What is cohesion?
The strong attraction between water molecules due to hydrogen bonds.
Why are the cohesive properties of water good?
Cohesion produces surface tension where water meets air.
Used for transpiration in plants and allows creatures to skate and settle on surface of water.
Why is water an ideal habitat?
It is a highly stable environment that does not change easily.
What % of the human body is made up of water?
60-70%
What bond is formed between amino acids?
Peptide bonds
What are proteins?
A diverse group of large and complex polymer molecules, made up of long chains of amino acids
What bond is formed between amino acids?
Peptide bonds
What forms when many amino acids are joined together?
Polypeptide
What enzyme catalyses the reaction between amino acids?
Peptidyl transferase
Give three examples of monosaccharides in order of sweetness (high to low)
Fructose
Glucose
Galactose
What is a sugar with 5 carbon atoms called?
Pentose sugar
Give two important pentose sugars
Ribose (in RNA nucleotides)
Deoxyribose (in DNA nucleotides)
What is formed when 2 monosaccharides join together?
A disaccharide
What do two glucose monosaccharides form?
Maltose
What do glucose and fructose form?
Sucrose (table sugar)
What do glucose and galactose form?
Lactose (in milk)
What is a polysaccharide?
2+ monosaccharides joined by glycosidic bonds
Give 4 examples of polysaccharides
Starch
Glycogen
Cellulose
Chitin
How are glycosidic bonds formed?
When OH groups from neighbouring monosaccharides undergo a condensation reaction to form a O-link between two monosaccharides
What is released during a condensation reaction?
Water
How do you break a glycosidic bond?
By hydrolysis
What type of monosaccharide is glucose?
Hexose
Why is energy released from glucose useful in cellular respiration?
Helps make ATP
Properties of glucose?
Polar and soluble in water
What is starch?
The main energy store in plants
Where is starch stored in plants?
In the seeds
Why is starch’s insolubility good?
Does not change water potential in cell
What are the two polysaccharides starch is made from?
Amylose and amylopectin
What is glycogenolysis?
When blood glucose levels decrease, glycogen is broken down to release glucose
What is glycogen stored as?
Small granules, especially in muscles and liver
What is the most abundant natural polymer?
Cellulose
What is the function of cellulose?
Main part of plant cell walls. Microfibrils provide structural support
What is the structure of cellulose?
Long straight chain of beta glucose
Why is the straight chain structure of cellulose good?
Makes it very strong meaning it prevents cells bursting when they take in excess water
What are microfibrils?
String fibres made of cellulose chains held together by hydrogen bonds
What do microfibrils join together to make?
Macrofibrils
What do macrofibrils join together to form?
Fibres
Properties of fibres?
Strong and insoluble
What gives structural stability in cellulose?
Hydrogen bonds formed between hydroxyl groups on adjacent parallel chains
Which polysaccharide cannot be broken down by human digestive enzymes?
Cellulose
What does cellulose form in our diet?
Very hard to break down into monomers so forms ‘fibres’ or ‘roughage’ necessary for a healthy digestive system
What’s special about the bonding of beta glucose monomers?
Alternate glucose monomers turn upside down to ensure hydroxyl groups are on the same side (top or bottom)
What happens when stored glucose is needed for respiration?
Biochemical energy in stored nutrients is converted into a useable energy source for cell
What reaction does starch/glycogen undergo to release glucose?
Hydrolysis
What is required for a hydrolysis reaction?
Water molecules
What elements do nucleic acids contain?
Carbon, hydrogen, oxygen, nitrogen and phosphorus
What does a nucleotide contain?
A pentose monosaccharide (sugar)
A phosphate group- an inorganic molecule that is acidic and negatively charged
A nitrogenous base- complex molecule containing one or two carbon rings in its structure as well as nitrogen
Many nucleotides= nucleic acid
What polymer is formed when nucleotides are linked together by condensation reactions?
Polynucleotide
How do nucleotides link together?
Phosphate group at fifth carbon of pentose sugar of one nucleotide forms a covalent bond with the hydroxyl group at the third carbon of the pentose sugar of the adjacent nucleotide. These bonds are called phosphodiester bonds.
What do linked nucleotides form?
A long, strong sugar-phosphate backbone with a base attached to each sugar.
How are individual nucleotides released from a nucleic acid?
Phosphodiester bonds are broken by hydrolysis.
What does DNA stand for?
Deoxyribonucleic acid.
What is the sugar in DNA?
Deoxyribose. (Fewer oxygen atoms than ribose)
What are the two groups of bases?
Pyrimidines and purines.
What are the two pYrimidines? And what is their structure?
ThYmine and cYtosine- contain single carbon ring structures.
What are the two purines?
Adenine and guanine- contain double carbon ring structures.
What is the DNA double helix?
Two strands of polynucleotides coiled into a helix.
Two strands held together by hydrogen bonds.
Each strand has phosphate groups at one end and OH group at other end.
Parallel strands arranged so that they run in opposite directions- they are antiparallel.
What are the bonds between bases in a DNA molecule?
Hydrogen bonds.
What does adenine pair with?
Thymine.
How many bonds can adenine and thymine both form?
2
How many bonds can both cytosine and guanine both form?
3
What base does cytosine pair with?
Guanine.
What does RNA stand for?
Ribonucleic acid.
What does RNA do?
Plays an essential role in the transfer of genetic information from DNA to the proteins that make up the enzymes and tissues of the body.
How are RNA nucleotides different to DNA nucleotides?
RNA have ribose as the pentose sugar rather than deoxyribose and thymine base is replaced with uracil.
What is uracil?
A pyrimidine that forms two hydrogen bonds with adenine.
What happens to the RNA molecules after protein synthesis?
They are degraded in the cytoplasm. The phosphodiester bonds are hydrolysed and the RNA nucleotides are released and reused.
Why do cells divide?
To produce more cells needed for growth or repair of tissues.
What do two daughter cells produced as a result of cell divisions contain?
DNA with a base sequence identical to the original parent cell.
What is semi-conservative replication?
- DNA helicase breaks hydrogen bonds between two polynucleotide DNA strands causing them to separate.
- Free-floating DNA nucleotides join to the exposed complementary bases on each original template strand.
- Activated nucleotides line up and are joined together by DNA polymerase. Hydrogen bonds form between the strands and strands twist to form a double helix.
- Sugar phosphate backbone is formed by covalent bonds between the phosphate of one nucleotide and the deoxyribose sugar of the next.
- Two new DNA molecules formed. Each new DNA molecule contains one strand from original molecule and one newly formed molecule (semi-conservative replication).
What causes a mutation?
Sequences of bases are not always matched exactly, and an incorrect sequence may occur in the newly copied strand. These errors occur randomly and spontaneously and lead to a change in the sequence of bases, known as a mutation.
What is the genetic code?
The sequence of bases along its DNA. Contains thousands of sections called genes of cistrons. Each gene codes for a specific polypeptide.
How was replication proven to be semi-conservative?
All bases in DNA contain Nitrogen and Nitrogen has two forms: light (14N) and heavy (15N).
Bacteria will incorporate nitrogen from their growing medium into any new DNA they make.
1. Grow bacteria in 15 N, 15N strand (2 strands of 15N) is heavy so makes a band low down the test tube.
2. Transfer cells to 14N and grow for one generation. Hybrid of 15N/14N (one of each) formed so one band in middle of test tube.
3. Grow for second generation in 14N. Light DNA (14N) (2 strands of 14N) and hybrid DNA (15N/14N) (one of each) mean two bands in test tube- one high up and one in middle.
This proves that the DNA split and kept one original strand while free nucleotides joined to make the second strand.
What does helicase do?
Separates the two DNA strands before replication. (like scissors)
What does a single-strand bunting protein do?
Keeps the separated DNA strands apart during replication.
What does DNA polymerase do?
Catalyses the formation of a new polynucleotide chain. (like glue)
What does DNA ligase do?
Joins together short sections of the lagging strand.
What is a gene?
A section of DNA that contains the complete sequence of bases (codons) to code for an entire protein.
What is a triplet code?
A sequence of three bases, called a codon. Each codon codes for one amino acid.
The code in the base sequences is a triplet code.
How many regularly occurring amino acids are there in biological proteins?
20
What is meant by the degenerate code?
Many amino acids can be coded for by more than one codon.
E.g, GAT GAA GAC and GAG all code for leucine.
What is a start codon?
Signals the start of a sequence that codes for a protein.
What do the three stop codons do?
Signal the end of the sequence.
What does having a single codon to signal the start of a sequence ensure?
The codons are read ‘in frame’. The DNA base sequence is ‘read’ from base 1, rather than base 2 or 3. So the genetic code is non-overlapping.
What is RNA?
A single-stranded chain of nucleotides.
What do cellular organisms use mRNA for?
Conveying genetic information that directs synthesis of specific proteins.
What sugar is present in mRNA and tRNA?
Ribose
What bases are present in mRNA and tRNA?
A G U C
How many DNA nucleotide bases code for a single amino acid?
3
Which nucleotide bases are common to DNA and RNA?
Adenine, guanine and cytosine.
Why is complementary base pairing important in DNA replication?
DNA can be replicated without error. Same sequence of nucleotides is produced.
Refuses occurrence of mutation.
Allows formation of hydrogen bonds.
Why is glucose well suited to its function in living organisms?
Soluble so easily transported.
Small so can diffuse across membranes.
Easily broken down to release energy.
Molecules can join to produce polysaccharides e.g. glycogen.
What types of activity to cells require energy for?
Synthesis
Transport
Movement
How is energy release from ATP?
Energy stored in phosphate bond- ATP broken down into ADP and inorganic phosphate. Energy released from the phosphate bond and used by cell.
What is ATP made up of?
Ribose sugar.
Adenine.
3 phosphate groups.
What does ADP made up of?
Adenine.
Ribose.
2 phosphate groups.
What’s messenger RNA?
Made in the nucleus.
Carries genetic code from DNA in nucleus to cytoplasm, where it’s used to make a protein during translation.
What is transfer RNA?
Found in cytoplasm.
Has an amino acid binding site at one end and a sequence of three bases at the other end (anticodon).
Carries amino acids that are used to make proteins to the ribosomes during translation.
What happens in translation?
- mRNA binds to small subunit of ribosome at its start codon.
- tRNA with complementary anticodon binds to mRNA start codon. Carries corresponding amino acid.
- tRNA with complementary anticodon to next codon and carrying the corresponding amino acid binds to the next codon on the mRNA.
- Peptide bond forms between two amino acids, catalysed by peptide transferase.
- Ribosome moves along mRNA, releasing first tRNA.
- Process continues, producing polypeptide chain until stop codon in mRNA and polypeptide is released. Results in primary structure of protein.
What is glycine?
The smallest amino acid- the R group is a hydrogen atom.
What are the properties of ATP?
Small- moves easily into/out of cells.
Water soluble- energy-requiring processes happen in aqueous environments.
Contains bonds between phosphates with intermediate energy: large enough to be useful for cellular reactions but not so large that every is not wasted as heat.
Releases energy in small quantities- quantities are suitable to mist cellular needs, so energy not wasted as heat.
Easily regenerated- can be recharged with energy.
What does ATP stand for?
Adenosine triphosphate.
